Improved performance of non-fullerene polymer solar cells by simple structural change of asymmetric acceptor based on indenothiophene

In this study, we have synthesized a new asymmetric n-type semiconducting molecule (Me-ITBD) by combining 4,4-bis(4-hexylphenyl)-7-methyl-6-(thiophen-2-yl)-4H-indeno thiophene with 2-(benzo [c] [1,2,5]-thiadiazol-4-yl methylene)-malononitrile and applied it to polymer solar cells. Compared to the PhITBD acceptor without methyl substituent in the 7-position of the core, Me-ITBD showed a larger torsional angle between thiophene and indenothiophene. Non-fullerene polymer solar cells (PSCs) with the methyl-substituted asymmetric acceptor Me-ITBD displayed an enhanced power conversion efficiency (PCE) of 5.75%, compared to the PSC (PCE = 1.79%) based on a PhITBD acceptor. The higher PCE value of the Me-ITBD-based PSC was ascribed to its improved device parameters, i.e. the J(sc) and FF, induced by a favorable fine morphology in the active layer. By simply introducing a methyl substituent in the indenothiophene unit of the PhITBD acceptor, the PSC performance was enhanced.